diff --git a/pkg/rest/client/apiv1_client.go b/pkg/rest/client/apiv1_client.go
index ce8990a..5a50c56 100644
--- a/pkg/rest/client/apiv1_client.go
+++ b/pkg/rest/client/apiv1_client.go
@@ -6,7 +6,6 @@ import (
 	"fmt"
 	"net/http"
 	"net/url"
-	"time"
 
 	"github.com/inbucket/inbucket/v3/pkg/rest/model"
 )
@@ -18,15 +17,22 @@ type Client struct {
 
 // New creates a new v1 REST API client given the base URL of an Inbucket server, ex:
 // "http://localhost:9000"
-func New(baseURL string) (*Client, error) {
+func New(baseURL string, opts ...Option) (*Client, error) {
 	parsedURL, err := url.Parse(baseURL)
 	if err != nil {
 		return nil, err
 	}
+
+	mergedOpts := getDefaultOptions()
+	for _, opt := range opts {
+		opt.apply(mergedOpts)
+	}
+
 	c := &Client{
 		restClient{
 			client: &http.Client{
-				Timeout: 30 * time.Second,
+				Timeout:   mergedOpts.timeout,
+				Transport: mergedOpts.transport,
 			},
 			baseURL: parsedURL,
 		},
diff --git a/pkg/rest/client/apiv1_client_opts.go b/pkg/rest/client/apiv1_client_opts.go
new file mode 100644
index 0000000..49fd67c
--- /dev/null
+++ b/pkg/rest/client/apiv1_client_opts.go
@@ -0,0 +1,38 @@
+package client
+
+import (
+	"net/http"
+	"time"
+)
+
+// options is a struct that holds the options for the rest client
+type options struct {
+	transport http.RoundTripper
+	timeout   time.Duration
+}
+
+type Option interface {
+	apply(*options)
+}
+
+func getDefaultOptions() *options {
+	return &options{
+		timeout: 30 * time.Second,
+	}
+}
+
+type transportOption struct {
+	transport http.RoundTripper
+}
+
+func (t transportOption) apply(opts *options) {
+	opts.transport = t.transport
+}
+
+// WithOptTransport sets the transport for the rest client.
+// Transport specifies the mechanism by which individual
+// HTTP requests are made.
+// If nil, http.DefaultTransport is used.
+func WithOptTransport(transport http.RoundTripper) Option {
+	return transportOption{transport}
+}
diff --git a/pkg/rest/client/apiv1_client_test.go b/pkg/rest/client/apiv1_client_test.go
index 22eb2f5..f7f84e2 100644
--- a/pkg/rest/client/apiv1_client_test.go
+++ b/pkg/rest/client/apiv1_client_test.go
@@ -1,6 +1,8 @@
 package client_test
 
 import (
+	"bytes"
+	"io"
 	"net/http"
 	"net/http/httptest"
 	"testing"
@@ -210,6 +212,33 @@ func TestClientV1GetMessageSource(t *testing.T) {
 	}
 }
 
+func TestClientV1WithCustomTransport(t *testing.T) {
+	// Call setup, passing a custom roundtripper and make sure it was used during the request.
+	mockRoundTripper := &mockRoundTripper{ResponseBody: "Custom Transport"}
+	c, router, teardown := setup(client.WithOptTransport(mockRoundTripper))
+
+	defer teardown()
+
+	router.Path("/api/v1/mailbox/testbox/20170107T224128-0000/source").Methods("GET").
+		Handler(&jsonHandler{json: `message source`})
+
+	// Method under test.
+	source, err := c.GetMessageSource("testbox", "20170107T224128-0000")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	want := mockRoundTripper.ResponseBody
+	got := source.String()
+	if got != want {
+		t.Errorf("Source got %q, want %q", got, want)
+	}
+
+	if mockRoundTripper.CallCount != 1 {
+		t.Errorf("RoundTripper called %v times, want 1", mockRoundTripper.CallCount)
+	}
+}
+
 func TestClientV1DeleteMessage(t *testing.T) {
 	// Setup.
 	c, router, teardown := setup()
@@ -337,11 +366,24 @@ func TestClientV1MessageHeader(t *testing.T) {
 	}
 }
 
+type mockRoundTripper struct {
+	ResponseBody string
+	CallCount    int
+}
+
+func (m *mockRoundTripper) RoundTrip(req *http.Request) (*http.Response, error) {
+	m.CallCount++
+	return &http.Response{
+		StatusCode: http.StatusOK,
+		Body:       io.NopCloser(bytes.NewBufferString(m.ResponseBody)),
+	}, nil
+}
+
 // setup returns a client, router and server for API testing.
-func setup() (c *client.Client, router *mux.Router, teardown func()) {
+func setup(opts ...client.Option) (c *client.Client, router *mux.Router, teardown func()) {
 	router = mux.NewRouter()
 	server := httptest.NewServer(router)
-	c, err := client.New(server.URL)
+	c, err := client.New(server.URL, opts...)
 	if err != nil {
 		panic(err)
 	}